1. Field of the Invention
The present invention relates to the advantageous structure of a cooling water passage in a water-cooled in-line type multi-cylinder engine.
2. Description of the Background Art
A cooling structure of a water-cooled in-line type two-cylinder engine is described in Japanese Utility model publication Hei 1-21161. In this example, a collecting passage for the cooling water is provided between both cylinders integrally with the cylinder head, and a thermostat is attached on the outlet of this collective passage.
Moreover, some in-line type multi-cylinder engines such as a four-cylinder engine may have a structure in which both ends of the water outlet side passage provided on another body separate from the cylinder head are communicated to the cylinder side water passage on both ends and joined together on the thermostat section provided on the center section.
Since the piping sections leading to the thermostat will increase if the water outlet side passage is provided outside the cylinder head, it would be preferable to form the water outlet side passage integrally with the cylinder head as shown in the conventional example. However, if this structure is applied to the in-line type four-cylinder engine, the water outlet side passages between cylinders converge on the thermostat section so that the flow of the cooling water is bound to be nonuniform. There is thus a desire to solve this problem in order to improve the cooling performance.